Method of reducing oxygen content in ECP solution

ABSTRACT

A novel method, which is suitable to substantially reduce the presence of oxygen micro-bubbles in an electroplating bath solution, is disclosed. The method includes the addition of aerobic bacteria to the electroplating bath solution to consume oxygen in the solution. Reduction of the oxygen content in the electroplating bath solution prevents oxygen micro-bubbles from forming in the solution and becoming trapped between the solution and the surface of a metal seed layer on a substrate to block the electroplating of a metal film onto the seed layer. Consequently, the presence of surface pits and other structural defects in the surface of the electroplated metal film is substantially reduced.

FIELD OF THE INVENTION

The present invention relates to electrochemical plating (ECP) processesused to deposit metal layers on semiconductor wafer substrates in thefabrication of semiconductor integrated circuits. More particularly, thepresent invention relates to a method of reducing the oxygen content ofan electroplating bath solution by adding aerobic bacteria to thesolution in order to enhance the quality of an electroplated metal film.

BACKGROUND OF THE INVENTION

When a copper layer is deposited on a substrate, such as byelectrochemical plating, the copper layer must be deposited on a metalseed layer such as copper, which is deposited on the substrate prior tothe copper ECP process. Conventional electrochemical plating techniquestypically use copper sulfate (CuSO₄) for the main electrolyte in theelectroplating bath solution. The solution may further include additivessuch as chloride ion and levelers, as well as accelerators andsuppressors, which increase and decrease, respectively, the rate of theelectroplating process. The rate of deposition of copper on thesubstrate, and the quality and resulting electrical and mechanicalproperties of the metallization, are critically dependent on theconcentration of these organic additives in the electroplating bathsolution.

Throughout the electroplating process, the electroplating bath solutionis continually circulated from and back to the bath container,respectively. This circulation of the solution often induces theformation of oxygen micro-bubbles in the solution. The micro-bubblestend to become trapped at various locations on the seed layer depositedon the wafer and block deposition of the metal film onto the seed layerat those locations. As a result, the metal film is unevenly plated onthe seed layer. During subsequent chemical mechanical planarization(CMP) of the electroplated metal film, this phenomenon is manifested bythe presence of defects in the form of pits, voids, broken metal linesand other defects in device features on the wafer. The presence of pits,voids and broken metal lines in device features leads to unreliable,unpredictable and unuseable electronic devices in the electronic circuitcontaining the features. Accordingly, a novel method is needed to reducethe oxygen content in an electrochemical plating bath solution in orderto prevent or at least reduce the formation of bubble-induced defects ina metal film or line electroplated onto a wafer.

SUMMARY OF THE INVENTION

In accordance with these and other objects and advantages, the presentinvention is generally directed to a novel method, which is suitable tosubstantially reduce the presence of oxygen micro-bubbles in anelectroplating bath solution. The method includes the addition ofaerobic bacteria to the electroplating bath solution to consume oxygenin the solution. Reduction of the oxygen content in the electroplatingbath solution prevents oxygen micro-bubbles from forming in the solutionand becoming trapped between the solution and the surface of a metalseed layer on a substrate to block the electroplating of a metal filmonto the seed layer. Consequently, the presence of surface pits andother structural defects in the surface of the electroplated metal filmis substantially reduced.

The present invention is further directed to a metal film having asubstantially reduced number of surface pits, voids and other defects.The metal film is plated onto a substrate by providing anelectrochemical plating solution, adding aerobic bacteria to thesolution, immersing the substrate in the solution, and carrying out anelectroplating process in the solution.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood, by way of example, withreference to the accompanying drawings, in which:

FIG. 1 is a schematic of an electrochemical plating system inimplementation of the present invention;

FIG. 1A is a cross-sectional view of a wafer substrate with a metal filmelectroplated thereon according to the method of the present invention;

FIG. 2 is a flow diagram illustrating a typical flow of process stepscarried out according to the method of the present invention; and

FIG. 3 is a graph in which the concentration of dissolved oxygen (DO) inan electroplating bath solution to which aerobic bacteria have beenadded is compared to the concentration of dissolved oxygen in anelectroplating bath solution devoid of aerobic bacteria.

DETAILED DESCRIPTION OF THE INVENTION

The present invention has particularly beneficial utility in theelectrochemical plating of a high-quality copper film on a copper seedlayer deposited on a semiconductor wafer substrate in the fabrication ofsemiconductor integrated circuits. However, the invention is moregenerally applicable to the electrochemical plating of metals includingbut not limited to copper on substrates in a variety of industrialapplications including but not limited to semiconductor fabrication.

The present invention is generally directed to a novel method forsubstantially reducing the presence of oxygen micro-bubbles in anelectroplating bath solution used to electroplate a metal film on a seedlayer provided on a substrate. The method facilitates the electroplatingof a metal film which is substantially devoid of voids and surface pitsonto the seed layer. According to the method, an aerobic bacteria isadded to the electroplating bath solution. The aerobic bacteria consumesall or most of the oxygen in the solution to prevent or reduce theformation of oxygen micro-bubbles in the solution typically as thesolution is circulated through the bath container. Consequently,micro-bubble blockage of metal electroplated onto the seed layer isprevented or at least substantially reduced.

The present invention is further directed to a metal film having asubstantially reduced number of surface pits, voids and other defects.The metal film is plated onto a substrate by providing anelectrochemical plating solution, adding aerobic bacteria to thesolution, immersing the substrate in the solution, and carrying out anelectroplating process in the solution.

The method of the present invention may be used with any formulation forthe electrochemical plating bath solution, such as copper, aluminum,nickel, chromium, zinc, tin, gold, silver, lead and cadmiumelectrochemical plating baths. The present invention is also suitablefor use with electrochemical plating baths containing mixtures of metalsto be plated onto a substrate.

It is preferred that the electroplating bath be a copper alloyelectroplating bath, and more preferably, a copper electroplating bath.Typical copper electroplating bath formulations are well known to thoseskilled in the art and include, but are not limited to, an electrolyteand one or more sources of copper ions. Suitable electrolytes include,but are not limited to, sulfuric acid, acetic acid, fluoroboric acid,methane sulfonic acid, ethane sulfonic acid, trifluormethane sulfonicacid, phenyl sulfonic acid, methyl sulfonic acid, p-toluenesulfonicacid, hydrochloric acid, phosphoric acid and the like. The acids aretypically present in the bath in a concentration in the range of fromabout 1 to about 300 g/L. The acids may further include a source ofhalide ions such as chloride ions.

Suitable sources of copper ions include, but are not limited to, coppersulfate, copper chloride, copper acetate, copper nitrate, copperfluoroborate, copper methane sulfonate, copper phenyl sulfonate andcopper p-toluene sulfonate. Such copper ion sources are typicallypresent in a concentration in the range of from about 10 to about 300g/L of electroplating solution.

Aerobic bacteria which are suitable for implementation of the presentinvention include nitrifying bacterial agents, Bdellovibriobacteriovorus, Acinetobacter calcoaceticus, Pseudamonas fluorescens,Arthrobacter globiformis, and Acetobacter pasteurianus. In a preferredembodiment of the present invention, the aerobic bacteria is anitrifying bacterial agent. Preferably, the aerobic bacteria are presentin the electroplating bath solution in a concentration of from typicallyabout 1 ml/l to about 5 ml/l.

Other electrochemical plating process conditions suitable forimplementation of the present invention include a plating rpm of fromtypically about 0 rpm to about 500 rpm; a plating current of fromtypically about 0.2 mA/cm² to about 20 mA/cm²; and a bath temperature offrom typically about 10 degrees C. to about 35 degrees C. In cases inwhich planarity of the electroplated metal through chemical mechanicalplanarization (CMP) is necessary, a leveling agent may be added to theelectroplating bath solution at a concentration of from typically about5 mmol/L to about 5 mol/L.

Referring to FIG. 1, an electrochemical plating (ECP) system 10 which issuitable for implementation of the present invention is shown. Thesystem 10 may be conventional and includes a standard electroplatingcell having an adjustable current source 12, a bath container 14, atypically copper anode 16 and a cathode 18, which cathode 18 is thesemiconductor wafer substrate that is to be electroplated with copper.The anode 16 and cathode/substrate 18 are connected to the currentsource 12 by means of suitable wiring 38. The bath container 14 holds anelectrolyte electroplating bath solution 20. The system 10 may furtherinclude a mechanism for rotating the substrate 18 in the bath 20 duringthe electroplating process, as is known by those skilled in the art.

The ECP system 10 may further include a pair of bypass filter conduits24, a bypass pump/filter 30, and an electrolyte holding tank 34. Thebypass filter conduits 24 typically extend through the anode 16 and opento the upper, oxidizing surface 22 of the anode 16 at opposite ends ofthe anode 16. The bypass filter conduits 24 connect to the bypasspump/filter 30 located outside the bath container 14, and the bypasspump/filter 30 is further connected to the electrolyte holding tank 34through a tank inlet line 32. The electrolyte holding tank 34 is, inturn, connected to the bath container 14 through a tank outlet line 36.It is understood that the ECP system 10 heretofore described representsjust one example of a possible system which is suitable forimplementation of the present invention, and other systems ofalternative design may be used instead.

Referring to FIGS. 1, 1A and 2, according to the method of the presentinvention, a metal seed layer 19, such as copper, is deposited on awafer substrate 18, as indicated in step S1 of FIG. 2. The metal seedlayer 19 may be deposited on the substrate 18 using conventionalchemical vapor deposition (CVD) or physical vapor deposition (PVD)techniques, for example, according to the knowledge of those skilled inthe art. The seed layer 19 has a thickness of typically about 50˜1500angstroms.

As indicated in step S2 of FIG. 2, the electrochemical plating (ECP)electrolyte bath solution 20 is prepared in the bath container 14. Theelectroplating bath solution 20 may include an accelerator having aconcentration of from typically about 5 mmol/L to about 5 mol/L, and mayinclude a leveling agent or additive in a concentration of fromtypically about 5 mmol/L to about 5 mol/L, as heretofore noted.

Next, as indicated in step S3 and shown in FIG. 1, the aerobic bacteria25 of the present invention is added to the electroplating bath solution20, which is then circulated from the bath container 14, through theelectrolyte holding tank 34 and back to the bath container 14, byoperation of the pump 30, to achieve an aerobic bacteria concentrationof from typically about 1 ml/l to typically about 5 ml/l in theelectroplating bath solution 20. The anode 16 and substrate 18 are thenimmersed in the bath solution 20 and connected to the adjustable currentsource 12, typically through wiring 38. Accordingly, the seed layer 19on the substrate 18 contacts the bath solution 20. The entire surface ofthe seed layer 19, as well as gap features on the substrate 18, isthoroughly wetted by the bath solution 20.

As indicated in step S4 of FIG. 2, the bath 20 is continually circulatedfrom the bath container 14 through the bypass filter conduits 24,electrolyte holding tank 34 and back into the bath container 14,respectively, by operation of the pump 30. This maintains the coppersulfate or other electrolyte in a dissolved state in the electroplatingbath solution 20, and prevents or minimizes precipitation of theelectrolyte onto the sides, bottom and other surfaces of the bathcontainer 14, throughout the electroplating process.

During circulation of the bath solution 20 throughout the ECP system 10,as heretofore described, dissolved oxygen normally forms oxygenmicro-bubbles (not shown) in the bath solution 20. Accordingly, theaerobic bacteria 25, having been previously added to the bath solution20 at step S3 of FIG. 2, consume all or most of the oxygen present inthe bath solution 20. This eliminates or substantially reduces thequantity of oxygen micro-bubbles which form in the solution 20.Consequently, the presence of micro-bubbles between the bath solution 20and the seed layer 19 on the substrate 18 is eliminated or substantiallyreduced during the subsequent electroplating process, which will behereinafter described.

As the electroplating bath solution 20 is circulated through the system10, a metal film 21 is electroplated onto the seed layer 19, as shown inFIG. 1A and indicated in step S5 of FIG. 2, typically as follows. Theelectroplating bath solution 20 is maintained at a temperature of fromtypically about 10 degrees C. to about 35 degrees C. The plating rpm forthe substrate 18 is typically about 0-500 rpm.

During the electrochemical plating process, the current source 12applies a selected voltage potential, typically at room temperature,between the anode 16 and the cathode/substrate 18. This voltagepotential creates a magnetic field around the anode 16 and thecathode/substrate 18, which magnetic field affects the distribution ofthe copper ions in the bath solution 20. In a typical copperelectroplating application, a voltage potential of about 2 volts may beapplied for about 2 minutes, and a plating current of from typicallyabout 0.2 mA/cm² to about 20 mA/cm² flows between the anode 16 and thecathode/substrate 18.

Consequently, copper is oxidized typically at the oxidizing surface 22of the anode 16 as electrons harvested from the copper anode 16 flowthrough the wiring 38 and reduce the ionic copper in the typicallycopper sulfate solution bath solution 20 to form a copper electroplate(not illustrated) at the interface between the cathode/substrate 18 andthe copper sulfate bath 20. Due to the absence or paucity of oxygenmicro-bubbles between the bath solution 20 and the surface of the seedlayer 19, the electroplated metal film 21 deposited onto the seed layer19 is substantially continuous and devoid of structural deformities suchas voids, pits and broken metal lines. Accordingly, the electroplatedmetal film 21 on the substrate 18 contributes to the fabrication ofhigh-quality IC devices that are characterized by high structural andoperational integrity.

Referring next to the graph of FIG. 3, which illustrates a graph inwhich the concentration of dissolved oxygen (DO) in an electroplatingbath solution to which aerobic bacteria have been added is compared tothe concentration of dissolved oxygen in an electroplating bath solutiondevoid of aerobic bacteria. From a consideration of the graph, it can beseen that the addition of aerobic bacteria to an electroplating bathsolution is capable of reducing the concentration of dissolved oxygen(DO) in the solution from about 5 mg/l to about 2 mg/l.

While the preferred embodiments of the invention have been describedabove, it will be recognized and understood that various modificationscan be made in the invention and the appended claims are intended tocover all such modifications which may fall within the spirit and scopeof the invention.

1. A method of electroplating a thin film onto a substrate, comprising:providing an electroplating bath solution; providing aerobic bacteria insaid solution; providing a current source in electrical contact withsaid substrate; immersing said substrate in said solution; and platingthe thin film onto said substrate by applying a current to saidsubstrate.
 2. The method of claim 1 wherein said aerobic bacteria is anitrifying bacterial agent, Bdellovibrio bacteriovorus, Acinetobactercalcoaceticus, Pseudamonas fluorescens, Arthrobacter globiformis, orAcetobacter pasteurianus.
 3. The method of claim 1 wherein said solutioncomprises copper sulfate.
 4. The method of claim 3 wherein said aerobicbacteria is a nitrifying bacterial agent, Bdellovibrio bacteriovorus,Acinetobacter calcoaceticus, Pseudamonas fluorescens, Arthrobacterglobiformis, or Acetobacter pasteurianus.
 5. The method of claim 1wherein said aerobic bacteria is present in said solution in aconcentration of about 1 ml/l to 5 ml/l.
 6. The method of claim 5wherein said aerobic bacteria is a nitrifying bacterial agent,Bdellovibrio bacteriovorus, Acinetobacter calcoaceticus, Pseudamonasfluorescens, Arthrobacter globiformis, or Acetobacter pasteurianus. 7.The method of claim 5 wherein said solution comprises copper sulfate. 8.The method of claim 7 wherein said aerobic bacteria is a nitrifyingbacterial agent, Bdellovibrio bacteriovorus, Acinetobactercalcoaceticus, Pseudamonas fluorescens, Arthrobacter globiformis, orAcetobacter pasteurianus.
 9. A method for forming a metal film onto asubstrate by: providing an electroplating bath solution comprising ametal; providing aerobic bacteria in a concentration of from about 1ml/l to about 5 ml/l; providing a current source in electrical contactwith said substrate; immersing said substrate in said solution; andapplying a current of from about 0.2 mA/cm² to about 20 mA/cm² to saidsubstrate.
 10. The metal film of claim 9 wherein said aerobic bacteriais a nitrifying bacterial agent, Bdellovibrio bacteriovorus,Acinetobacter calcoaceticus, Pseudamonas fluorescens, Arthrobacterglobiformis, or Acetobacter pasteurianus.
 11. The metal film of claim 9wherein said electroplating bath solution comprises copper sulfate. 12.An electrochemical plating solution comprising: an electrolyte solutioncomprising metal; and an aerobic bacteria provided in said electrolytesolution.
 13. The electrochemical plating solution of claim 12 whereinsaid metal is copper, aluminum, nickel, chromium, zinc, tin, gold,silver, lead, or cadmium.
 14. The electrochemical plating solution ofclaim 12 wherein said aerobic bacteria is a nitrifying bacterial agent,Bdellovibrio bacteriovorus, Acinetobacter calcoaceticus, Pseudamonasfluorescens, Arthrobacter globiformis, or Acetobacter pasteurianus. 15.The electrochemical plating solution of claim 12 wherein said aerobicbacteria is present in said electroplating bath solution in aconcentration of about 1 ml/l to 5 ml/l.
 16. The electrochemical platingsolution of claim 12 wherein said electroplating bath solution comprisescopper sulfate.